The present invention relates to a semiconductor optical function device. More specifically, the present invention relates to a semiconductor optical function device having a semiconductor optical waveguide.
FIG. 1 is a schematic perspective view showing a configuration of a conventional semiconductor optical function device 10. FIG. 2 is a schematic sectional view showing the conventional semiconductor optical function device 10 taken along a line 2-2 in FIG. 1. FIG. 3 is a schematic view showing the conventional semiconductor optical function device 10 in an operational state.
As shown in FIG. 1, the conventional semiconductor optical function device 10 includes an optical waveguide 28. The optical waveguide 28 has a recess portion with a semiconductor structure extending in a lateral direction thereof, and insulation layers 26 are formed in the recess portion. A non-waveguide region 29 without a recess portion is disposed at an end portion of the optical waveguide 28. The non-waveguide region 29 continuously extends outside the insulation layers 26. The non-waveguide region 29 has a semiconductor interface 32 extending in parallel to a substrate edge surface 30 on a side corresponding to the substrate edge surface 30.
When the conventional semiconductor optical function device 10 is produced, first, a first conductive type lower clad layer (formed of n-InP) 15, a core layer (formed of InGaAsP) 16, a second conductive type upper clad layer (formed of P-InP) 18, and a second conductive type contact layer (formed of P+-InGaAs) 20 are grown as crystal phases on a first conductive type substrate (formed of n-InP) 14. A total thickness of the second conductive type upper clad layer 18 and the second conductive type contact layer 20 is, for example, 2 μm.
In the next step, grooves (to be the insulation layers 26) are formed in both sides of a light passing portion (to be the optical waveguide 28) through a lithography technology. Afterward, a passivation film (formed of SiO2 or SiN) 22 is formed on the second conductive type contact layer 20 or a semiconductor layer. A mask pattern is designed in advance such that the grooves are not formed in the non-waveguide region 29 when the grooves are formed through the lithography technology. The grooves (to be the insulation layers 26) have a depth of about 2 μm corresponding to the total thickness of the second conductive type upper clad layer 18 and the second conductive type contact layer 20.
In the next step, an electrically insulation material (to be the insulation layers 26) such as an organic insulation film (formed of, for example, polyimide) is filled in the grooves (to be the insulation layers 26) and is flattened. Afterward, a second electrode (anode) 24 is formed on the passivation film 22. Further, a backside surface of the first conductive type substrate 14 is polished to have an appropriate thickness (normally, about 100 m), and a first electrode (cathode) 12 is formed on the backside surface thus polished. Afterward, the conventional semiconductor optical function device 10 is cut in an appropriate chip size. Note that an appropriate reflection film is formed on a cut edge surface (an outer side surface). For example, in a semiconductor optical amplifier, a non-reflection film is formed on an edge surface.
When the conventional semiconductor optical function device 10 having the optical waveguide 28 is in an operational state, residual reflection at the end portion of the optical waveguide 28 may generate light passing in a reverse direction (reverse light) as shown in FIG. 3. When the reverse light is generated, a function of the conventional semiconductor optical function device 10 may be interfered. A semiconductor optical modulator or a function element with an integrated semiconductor optical modulator (a semiconductor device) tends to be especially susceptible to the reverse light.
In the semiconductor optical amplifier, the residual reflection at an end portion of an optical waveguide may cause a resonance effect. In this case, a cyclic optical amplification gain corresponding to an optical length of the semiconductor optical amplifier becomes non-flat. The non-flatness of the optical amplification gain causes a large variance in a characteristic of an individual element, thereby lowering yield of a manufacturing process of the element. Further, the optical amplification gain tends to fluctuate in response to a subtle difference in a wavelength or a temperature, thereby causing instability in an optical system.
For example, in a semiconductor device, in which a semiconductor optical modulator and a semiconductor laser are integrated on a single substrate, laser light is continuously generated or oscillated in a semiconductor laser region and modulated in a semiconductor optical modulator region. Afterward, the laser light reaches an end portion of an optical waveguide.
At this moment, when the residual reflection occurs at the end portion of the optical waveguide, the reverse light is generated. The reverse light passes through the semiconductor optical modulator region and returns to the semiconductor laser region. Eventually, the residual light becomes a seed in the semiconductor laser region, thereby making the continuous oscillation state of the laser light unstable.
Further, a variance in a characteristic of an individual element becomes large, thereby lowering yield of a manufacturing process of the element. Further, a modulation response property tends to vary in response to a current of the semiconductor laser, thereby causing instability in an optical system.
In order to solve the problem described above, Non-Patent Reference has disclosed two countermeasures for reducing an amount of the reverse light. In the first one of the countermeasures, an optical waveguide has a curved shape with a specific curvature. In the second one of the countermeasures, a region having a width greater than that of the optical waveguide (a wide width end portion region) is disposed at the end portion of the optical waveguide. Accordingly, it is possible to prevent the reverse light generated at the end portion of the optical waveguide from returning to the optical waveguide.
Non-Patent Reference: “Wide range of operating conditions for a 1000 Km-2.5 Gb/s transmission with a new WDM optimized design for integrated laser-electroabsorption modulator”, Optical Fiber Communication 1999, WH1-1
In the conventional method disclosed in Non-Patent Reference, the reverse light itself generates multiple reflections at the wide width end portion region. A large portion of reflected light irradiates externally, thereby deteriorating quality of signal light.
According to Patent Reference 1, an optical waveguide has an edge surface disposed inside an edge surface of a substrate. Accordingly, it is possible to reduce an amount of reflected light from the edge surface of the substrate to a light source.
Patent Reference 1: Japanese Patent Publication No. 06-075130
According to Patent Reference 2, an optical waveguide has an edge surface disposed in an inclined state relative to an interface. Accordingly, it is possible to reduce an influence of reflected light on a light source.
Patent Reference 2: Japanese Patent Publication No. 05-027130
In the conventional technologies described above, however, efficiencies thereof are not sufficient, and it is difficult to effectively reduce the internal reflection due to the residual reflection at the end portion of the optical waveguide.
In view of the problems described above, an object of the present invention is to provide a semiconductor optical function device capable of solving the problems of the conventional semiconductor optical function device. In the present invention, it is possible to sufficiently reduce internal reflection due to residual reflection at an end portion of an optical waveguide.
Further objects and advantages of the invention will be apparent from the following description of the invention.